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@MastersThesis{Campos:2012:CaCoLí,
               author = "Campos, Leandro Zanella de Souza",
                title = "Caracteriza{\c{c}}{\~a}o das componentes-M e dos 
                         l{\'{\i}}deres de rel{\^a}mpagos naturais a partir de 
                         observa{\c{c}}{\~o}es de c{\^a}meras de alta 
                         resolu{\c{c}}{\~a}o temporal e medidas de campo el{\'e}trico",
               school = "Instituto Nacional de Pesquisas Espaciais",
                 year = "2012",
              address = "S{\~a}o Jos{\'e} dos Campos",
                month = "2012-03-01",
             keywords = "rel{\^a}mpagos, componentes-M, l{\'{\i}}deres, modelo 
                         bidirecional, lightning, M components, leaders, bidirectional 
                         leader model.",
             abstract = "O presente trabalho consiste em combinar observa{\c{c}}{\~o}es 
                         obtidas atrav{\'e}s de c{\^a}meras de v{\'{\i}}deo de alta 
                         resolu{\c{c}}{\~a}o temporal e medidas de campo el{\'e}trico 
                         atmosf{\'e}rico para estudar e caracterizar dois dos 
                         fen{\^o}menos relacionados aos rel{\^a}mpagos nuvem-solo 
                         naturais: l{\'{\i}}deres e componentes-M. Utilizando dados de 
                         redes de detec{\c{c}}{\~a}o de rel{\^a}mpagos de larga escala e 
                         aplicando t{\'e}cnicas de fotogrametria foi poss{\'{\i}}vel 
                         obter distribui{\c{c}}{\~o}es estat{\'{\i}}sticas da 
                         velocidade de propaga{\c{c}}{\~a}o de l{\'{\i}}deres 
                         escalonados (negativos), cont{\'{\i}}nuos e positivos, bem como 
                         analisar como ela evolui conforme eles se aproximam do solo. 
                         Observamos que a maior parte dos l{\'{\i}}deres positivos 
                         acelera ao longo de seu desenvolvimento, enquanto os 
                         l{\'{\i}}deres escalonados (negativos) desenvolvem velocidades 
                         que tendem a oscilar ao redor de um valor m{\'e}dio e os 
                         l{\'{\i}}deres cont{\'{\i}}nuos frequentemente desaceleram. 
                         Para os tr{\^e}s tipos mencionados n{\'o}s n{\~a}o encontramos 
                         qualquer correla{\c{c}}{\~a}o entre a velocidade m{\'e}dia do 
                         l{\'{\i}}der e o pico de corrente da descarga de retorno 
                         iniciada por ele. Por outro lado, foi poss{\'{\i}}vel mostrar 
                         que a velocidade dos l{\'{\i}}deres cont{\'{\i}}nuos depende 
                         do tempo transcorrido desde a descarga de retorno anterior, o que 
                         indica que eles sofrem uma grande influencia da condutividade 
                         remanescente ao longo do canal. Uma s{\'e}rie de estudos de caso 
                         de l{\'{\i}}deres e componentes-M foi realizada a partir da 
                         sincroniza{\c{c}}{\~a}o entre os registros obtidos pelas 
                         c{\^a}meras e os dados fornecidos pelos sensores de campo 
                         el{\'e}trico. Atrav{\'e}s deles foi poss{\'{\i}}vel notar que 
                         l{\'{\i}}deres escalonados e l{\'{\i}}deres positivos devem 
                         possuir distribui{\c{c}}{\~o}es semelhantes de cargas 
                         el{\'e}tricas, enquanto que l{\'{\i}}deres cont{\'{\i}}nuos 
                         aparentam ter uma estrutura bastante distinta. Pela primeira vez 
                         foi poss{\'{\i}}vel associar a ocorr{\^e}ncia de 
                         l{\'{\i}}deres de recuo (vis{\'{\i}}veis com o 
                         aux{\'{\i}}lio das c{\^a}meras de alta resolu{\c{c}}{\~a}o 
                         temporal) {\`a} produ{\c{c}}{\~a}o de pulsos de campo 
                         el{\'e}trico de curta dura{\c{c}}{\~a}o, da ordem de alguns 
                         microssegundos. Estes pulsos se assemelham bastante aos descritos 
                         em trabalhos anteriores que analisaram descargas K de 
                         rel{\^a}mpagos intranuvem e nuvem- solo, refor{\c{c}}ando a 
                         hip{\'o}tese de que ambos consistem em um mesmo fen{\^o}meno 
                         f{\'{\i}}sico. Observamos tamb{\'e}m casos especiais de 
                         l{\'{\i}}deres escalonados; dois eventos classificados como tipo 
                         \$\beta\$\$_{1}\$ e sete casos do tipo 
                         \$\beta\$\$_{2}\$. Finalmente, realizamos uma an{\'a}lise 
                         comparativa das componentes-M negativas e positivas, mostrando as 
                         diferen{\c{c}}as entre suas assinaturas de campo el{\'e}trico. 
                         Os resultados sugerem que as componentes-M negativas, normalmente 
                         precedidas por pulsos de curta dura{\c{c}}{\~a}o (da ordem de 
                         microssegundos), s{\~a}o iniciadas por l{\'{\i}}deres de recuo. 
                         ABSTRACT: The present work project consists in combining 
                         observations obtained from high-speed video cameras and 
                         atmospheric electric field measurements to study two physical 
                         phenomena involved in the production of natural cloud-to-ground 
                         lightning: leaders and M components. By using data from lightning 
                         locating systems and applying photogrammetry techniques it was 
                         possible to obtain statistical distributions of the propagation 
                         speed of negative stepped, dart and positive leaders, as well as 
                         analyze how they change as the leader approaches the ground. We 
                         have observed that the majority of positive leaders accelerate 
                         throughout their development, while stepped leaders present speeds 
                         that tend to oscillate around an average value and dart leaders 
                         most frequently decelerate. For the three leader types mentioned 
                         above we have found no correlation between average speed and the 
                         estimated return stroke peak current; on the other hand, dart 
                         leader average speeds depend strongly on the elapsed time since 
                         the previous return stroke, which indicates that they are strongly 
                         influenced by the remaining channel electric conductivity. Also, a 
                         series of case studies of leaders and M components was done based 
                         on synchronization of the high-speed camera recordings with the 
                         electric field sensor data. We noticed that stepped and positive 
                         leaders must have similar electric charge distributions, while 
                         dart leaders present a distinct structure. For the very first time 
                         it was possible to associate the occurrence of recoil leaders 
                         (visible through the camera records) to the production of short 
                         duration pulses, of the order of a few microseconds, and 
                         detectable by the fast electric field sensor. These pulses 
                         resemble those described in previous works that focus on K changes 
                         of intracloud and ground flashes, reinforcing the hypothesis that 
                         proposes that they are the same phenomenon. We have also analyzed 
                         special cases of stepped leaders; two events categorized as 
                         \$\beta\$\$_{1}\$ leaders and seven cases of 
                         \$\beta\$\$_{2}\$ leaders. This has induced us to propose a 
                         hypothesis to describe them in the context of the bidirectional 
                         leader model. Finally, we have done a comparative analysis between 
                         positive and negative M components, showing the differences in 
                         their electric field waveforms. The results suggest that negative 
                         M components are usually preceded by short duration pulses (of the 
                         order of microseconds), suggesting that they are initiated by 
                         recoil leaders.",
            committee = "Batista, Inez Staciarini (presidente) and Pinto, Iara Regina 
                         Cardoso de Almeida (vice-presidente) and Saba, Marcelo 
                         Magalh{\~a}es Fares (orientador) and Tavares, Fernanda S{\~a}o 
                         Sabbas and Lacerda, Moacir",
           copyholder = "SID/SCD",
         englishtitle = "Characterization of M components and leaders associated with 
                         natural lightning from high-speed video observations and electric 
                         field measurements",
             language = "pt",
                pages = "194",
                  ibi = "8JMKD3MGP7W/3BA2MDE",
                  url = "http://urlib.net/rep/8JMKD3MGP7W/3BA2MDE",
           targetfile = "publicacao.pdf",
        urlaccessdate = "24 jan. 2021"
}


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